Aluminum record blank



0a. 3, 1939. D, E Rbs 2,174,720.

ALUMINUM RECORD BLANK Filed July 25, 1936 RICINOLEIC Aclo ALUMINUM BASE ALUMINUM B455 INVENTOR. I

Patcntedoct. 3, 1939 UNITED STATES 2.174.720 AL ancoan BLANK Junius D. Edwards, Oakmont, Pa, assignor to Aluminum Company of America, Pittsburgh, Pa, a corporation of Pennsylvania Application July 25, 1936, Serial No. 92,596

It has been the practice to make sound recordings on aluminum discs by means of a diamond or sapphire stylus or its equivalent. The stylus is caused, by electrical means, to vibrate laterally with a frequency corresponding to the sound being recorded, while the aluminum disc is caused to revolve at a constant speed beneath the stylus. .The stylus is moved across the face of the disc at a uniform speed, so that it impresses a uniformly l0 spaced spiral groove in the surface of the disc.

The aluminum records so produced have advantages over other types of sound records; for example, they may be used directly for sound reproduction without the necessity of preparing master records in other materials.

For many uses the fidelity and tonal quality of reproduced sound is satisfactorily supplied by current methods of recording. The outstanding problem, however, has been to reduce excessive noise introduced by irregularities in the sound track other than those representing the recorded sound. These irregularities and the resultant noise in reproduction appear to be caused by a tearing action of the stylus during recording.

The proper function of the recording stylus is to press or rub" the sound groove into the metal without tearing or cutting the surface. It is possible, by proper shaping of the stylus and adjustment of the recording conditions, to produce a sound record on bare aluminum which is satisfactory for many requirements. It isalso possible. where the adjustment of the stylus does not represent optimum recording conditions, to reduce the background noise somewhat by lubricating the disc with mineral oil or paraffin, and this has been a common practice in the past. The demands of the art, however, have become so exacting that even these expedients have not been adequate where the highest tonal quality and freedom from '40 noise are demanded.

It is an object of the present invention to provide a'method of recording on aluminum for direct sound reproduction which will substantially reduce the background noise experienced with alu- 45 minum records as made by the best technique heretofore employed. More particularly, it is an According to the invention, the aluminum I permits the recording stylus to produce flow in-the metal without tearing or cutting. Under some conditions, when ricinoleic acid is used, it may fail, some time after application, to wet the surface, and this dimculty can be overcome by mixing 15 the ricinoleic acid with mineral oil in amount sufflcient to give a completely miscible mixture.

This treatment effects aireduction of noise level, in some cases, of as much as three or four decibels as determined by comparison with the best prior 20 practices in recording and reproduction.

Referring to the drawing, Fig. 1- is a plan view, and Fig. 2 is a sectional view, of a sound recording blank treated in accordance with my invention. It will be understood that, for the purposes of 25 illustration, the thickness of the coating is exaggerated in Fig. 2. Figure 3 is a fragmentary sectional view of a sound recording blank treated in accordance with my-invention, and with a sound groove or track impressed therein, the coating'also 80 being shown as exaggerated in this-figure.

The treated blank with the sound groove impressed therein may be played without further treatment, or it may be cleaned by any suitable rnethod and provided. with an artificially pro- 35 duced oxide coating carrying an adsorbed lubricant to improve its reproducing characteristics as disclosed in my United States Letters Patent No. 2,085,741, dated July 6, 1937, to provide an article such as that claimed in that patent.

,It will be understood that modification of the invention will be limited only as defined in the appended claims.

I claim:

1. A sound recording blank comprising an aluminum disc coated with a fatty acid having lubricating properties.

2. Around recording blank comprising an aluminum disc having ricinoleic acid thereon. 5o

3. A sound recording blank comprising an aluminum disc having on its surface a fatty acid having lubricating properties and characterized by the property of remaining in situ under the pressure exerted by a recording stylus.

8 D. EDWARDS. 

